ES2947761T3 - Optical quality molding compositions with increased heat resistance - Google Patents

Abstract

The present invention relates to a process for the manufacture of an acrylic copolymer that has greater heat resistance, high transparency and better adhesion to metal surfaces. The invention further relates to molding compositions containing this copolymer. The molding compositions of the present invention are very suitable for the manufacture of optical elements for optoelectronic devices comprising acrylic and metal or ceramic parts. (Automatic translation with Google Translate, without legal value)

Description

DESCRIPTION

Optical quality molding compositions with increased heat resistance

Technical field

The present invention relates to a process for the manufacture of acrylic molding compositions having increased heat resistance, excellent optical properties and improved adhesion to metals. Molding compositions of this type are well suited for the manufacture of optoelectronic devices comprising acrylic and metallic or ceramic components, for example, light emitting diodes (LEDs), LED lenses, light guides, optical sensors. , solar cells and various medical devices that have a light source.

Previous technique

Copolymers comprising repeating units derived from methyl methacrylate (hereinafter MMA), which, for reasons of simplicity, are often called acrylic molding compositions, are usually transparent materials having high weather resistance. Therefore, acrylic molding compositions are commonly used in applications where high transparency, low haze and high weather resistance are required. There is also an increasing demand for substantially colorless transparent polymers with particularly high heat resistance for optical applications including, e.g. e.g., light sources for indoor and outdoor use comprising high-power light-emitting diodes ( ^LEDs ). To increase the light output of an LED, the built-in optical lens of the LED is placed in close proximity to the light-emitting semiconductor element. The operating temperature of the LED surface, especially of so-called high-power white LEDs, often exceeds 100 °C or sometimes even 130 °C. It is therefore important that materials for these applications are substantially colorless and have high transparency and particularly low haze values, as well as high heat resistance.

Furthermore, optoelectronic devices such as ^LEDs , optical sensors or solar cells typically comprise transparent acrylic components and metallic or ceramic structural elements that are hermetically sealed together. A durable, strong and airtight adhesion (sealing) between the acrylic component and the metal or ceramic components is therefore of utmost importance to ensure long-term reliability and sustainability of the device, in particular if the device components are sensitive to traces of humidity and/or oxygen.

It is common general knowledge that the presence of free carboxylic acid and phosphonic acid functionalities in acrylic polymers is advantageous in terms of adhesion to metallic or ceramic substrates, because these functionalities react chemically with commonly used metallic or ceramic surfaces. For this reason, copolymers comprising repeating units derived from (meth)acrylic acid, for example copolymers of MMA and methacrylic acid (hereinafter MAA) are generally good candidates for use in optoelectronic devices. On the other hand, it is important that the cumulative content of MAA units and glutaric anhydride units in the copolymer does not exceed 20% by weight, preferably does not exceed 10% by weight, based on the weight of the copolymer to ensure that the copolymer has low water absorption. A high content of glutaric anhydride units in the copolymer relative to the MAA units often has increased optical haze.

Furthermore, copolymers comprising MAA units are commonly used as compatibilizers, adhesion promoters or reactive components. In these applications, a high content of MAA units is essential to achieve sufficient adhesion.

US 7,888,456 B2 describes a process for producing a thermoplastic copolymer, in which a copolymer containing unsaturated carboxylic acid alkyl ester units such as MMA and unsaturated carboxylic acid units such as MAA is produced and subsequently heat treated. to perform an intramolecular cyclization reaction to produce a thermoplastic copolymer containing glutaric anhydride units. The final product of US 7,888,456 B2 is reported to have a glass transition temperature of not less than 130°C, a high level of transparency and good heat resistance. However, as a consequence of the predominant formation of glutaric anhydride units, it has only a low content of MAA-derived repeating units and therefore only moderate adhesion to metal or ceramic surfaces.

EP 3239 191 A1 describes a process for producing a (meth)acrylic resin composition comprising continuously feeding a mixture of methyl methacrylate monomers, optional alkyl acrylates and other optional co-monomers into a tank reactor, performing the bulk polymerization at a conversion ratio of 40 to 70% and continuously feeding the liquid to a vented extruder to separate volatile components.

WO 97/33925 A1 describes a multi-step process for producing a heat-resistant poly(methyl methacrylate) molding composition, wherein the process encompasses radical polymerization of methyl methacrylate and optional co-monomers, p. e.g., alkyl acrylates, in at least two reactors. The first reactor is operated at a temperature below 120°C and the second reactor is operated at a temperature in the range of 130 to 200°C. Typically, unreacted monomers are separated in a subsequent vacuum degassing step and at least partially recycled in the polymerization process.

Document WO 2017/097979 A1 teaches a procedure for the preparation of a copolymer comprising MMA and MAA monomers. Examples from WO 2017/097979 A1 briefly mention that the raw polymer syrup after the polymerization step can be devolatilized at a temperature of 200 °C to 230 °C (extruder heating jacket temperature) in a degassing extruder to give the final copolymer. No information on the melting temperature of the copolymer is disclosed. The obtained copolymer is reported to be suitable for light guides, lenses, automobile moldings, automobile taillight and headlight parts, etc. No details are provided on the degassing stage.

Initial attempts by the inventors to reproduce the teachings of WO 2017/097979 A1 resulted in a copolymer with a high content of glutaric anhydride units and a low content of free carboxylic acid groups. Therefore, this copolymer had only moderate adhesion to metal or ceramic surfaces and was not suitable for the intended purpose.

It is well known that efficient degassing of a copolymer mixture obtained in a polymerization step typically employs high working temperatures to remove volatile components, in particular, unreacted monomers such as MMA and MAA. This stage is necessary because traces of components of this type in the final copolymer tend to decrease heat resistance and, in the case of MAA, cause corrosion of the extrusion or injection molding equipment. Additionally, they can lead to optical defects during the injection molding process due to foaming.

In MMA-MAA copolymers having 10 wt% or less MAA units in the copolymer chain, the formation of glutaric anhydride units results primarily from a reaction of adjacent MAA and MMA units, accompanied by the formation of methanol. In MMA-MAA copolymers having a higher content of MAA units in the copolymer chain, the formation of glutaric anhydride units from a reaction of two adjacent MAA units, accompanied by the formation of water, is also observed. It becomes an important secondary reaction at elevated temperatures. Traces of methanol and water, even if present in small quantities, tend to reduce the heat resistance of the final copolymer and can lead to surface defects during injection molding due to their partial vaporization.

The authors of the invention observed that between the last degassing zone of a degassing device such as a degassing extruder, in relation to the transport direction of the copolymer melt, and the outlet die of the melt, there are usually holds in which the copolymer melt still has a high temperature. As a consequence, glutaric anhydride, methanol and water units can be formed, which then remain in the final polymer. The withholdings are, e.g. e.g., areas in the degassing device after the last degassing zone in which a pressure is built up to press the copolymer melt through subsequent passages, melt filters or melt sieves and the die. outlet of the melt.

In order to minimize the unwanted formation of glutaric anhydride units, low temperatures and/or low residence times of the copolymer melt in the retentions after the last degassing zone of the extruder would therefore be advantageous. . However, under these conditions, the removal of volatile components such as unreacted methacrylic acid residues would be more difficult. Furthermore, an active cooling of the copolymer melt directly after the last degassing zone, relative to the transport direction of the copolymer melt, would lead to an increase in its melt viscosity and would make handling and processing more difficult. filtration of the copolymer melt. Due to the high viscosity of the copolymer melt, low radial mixing, limited heat transfer and low thermal conductivity, the possibilities of changing the temperature of the melt by means of heating or cooling elements after the degassing device They are limited.

Object of the present invention

Taking into account the above-described shortcomings, it was an object of the present invention to provide a process for the preparation of an acrylic copolymer having excellent optical properties, in particular low haze and substantially no yellow cast, high heat resistance and high content of free carboxylic acid groups and a low content of glutaric anhydride units. These properties would allow the use of the copolymer in optoelectronic devices, such as LEDs, optical lenses, light guides, optical sensors and solar cells that comprise a transparent acrylic component and a metallic or ceramic structural element and have a high working temperature on their surfaces. . Due to a high content of free carboxylic acid functionalities, the copolymer would have excellent adhesion to metal and ceramic surfaces and would allow a durable, strong and airtight adhesion between ^the acrylic and metal ^or ceramic components of devices of this type. Furthermore, it was desired that the cumulative content of MAA units and glutaric anhydride units in the copolymer should not exceed 20% by weight, preferably not exceed 10% by weight, based on the weight of the copolymer to ensure that the copolymer has a low water absorption.

Summary of the invention

In order to overcome the drawbacks of document WO 2017/097979 A1, the authors of the invention carried out an extensive study and, surprisingly, found that the content of free carboxylic acid groups in a copolymer that can be obtained through the polymerization of MMA and MAA can be increased dramatically by carefully adjusting the process conditions after the degassing step. In particular, it was found that when a copolymer mixture obtained in a polymerization step is devolatilized in a degassing unit comprising

at least one copolymer mixture feed hole,

at least one degassing device, the degassing device comprising

at least one degassing zone,

at least one gas outlet

at least one copolymer melt outlet,

and at least one melt outlet die,

It is crucial that the copolymer melt temperature Tv, °C (Tv given in °C) in the last degassing zone, relative to the transport direction of the copolymer melt, the copolymer melt temperature copolymer To, °C ( To given in °C) entering the melt outlet die and the total residence time t, ^s (t given in ^s ) of the copolymer melt between the last degassing zone and the melt outlet matrix of the degassing unit are adjusted in such a way that the term

is less than 8, preferably less than 6, even more preferably less than 4, particularly preferably less than 2. If the above term is greater than 8, substantial formation of glutaric anhydride units occurs so that the resulting copolymer has a reduced content of methacrylic acid units in relation to the content of monomeric methacrylic acid in the monomer mixture of polymerization step (a).

Under these procedural conditions, the unwanted intramolecular cyclization reaction that forms glutaric anhydride units from adjacent MAA units and MMA units in the copolymer can be efficiently suppressed so that the final copolymer has a particularly high content of free carboxylic acid groups. Additionally, the copolymer has high heat resistance and excellent optical properties, in particular low haze and substantially no yellow cast. The terms "high heat resistance" and "low heat resistance" as used herein indicate that the copolymer has a high/low Vicat softening temperature (ISO 306-B50).

Figure 1 schematically shows an example of a degassing unit used in the degassing stage (c):

1. degassing extruder

2. Copolymer blend feeding

3. Copolymer mixture feeding hole

4. last degassing zone (vacuum zone)

5 . last gas outlet

6. copolymer melt output

7. fusion output matrix

8. engine

9. Oopolymer melt

10. Melt filter (optional)

11. Other gas outlets (optional)

12. melt oonduoto

13. zone 1 (see Examples 1-3)

14. measurement zone (see Examples 1-3)

Detailed description of the invention

The process of the present invention comprises at least one polymerization step (a), followed by an optional heating step (b) and subsequently followed by a degassing step (o).

In the polymerization step (a), a mixture of monomers comprising 80.0 to 99.9% by weight, preferably 85.0 to 98.0% by weight, of MMA; and from 0.1 to 20.0% by weight, preferably from 2.0 to 8.0% by weight, of a compound represented by formula (I)

the substituent R1 being a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, preferably a methyl group;

optionally, from 0.0 to 19.9% by weight, preferably from 0.0 to 7.0% by weight of a monomer selected from methyl aorylate, ethyl aorylate or styrene;

a polymerization initiator;

and, optionally, an oadena transfer agent,

It undergoes radical oopolymerization in a polymerization reactor to form a mixture of oopolymers.

The term "copolymer blend", as used herein, refers to a mixture comprising the copolymer and the volatile components. "Volatile components" include MMA, the compound represented by formula (I), optionally, and a monomer selected from methyl aorylate, ethyl aorylate or styrene. Furthermore, the "volatile components" may optionally comprise a solvent, methanol and water.

The shape of the oopolymer mixture obtained in step (a) is not particularly limited and depends on the reaction conditions and the type of polymerization. The polymerization in step (a) may be a bulk polymerization, a solution polymerization, a dispersion polymerization or a suspension polymerization. Accordingly, the oopolymer mixture may be an oopolymer solution (sometimes also called oopolymer syrup), an oopolymer dispersion, or an oopolymer suspension.

In the optional heating step (b), the oopolymer mixture obtained in the polymerization step (a) is heated in a heating unit at a temperature of 100 °C to 300 °C.

Subsequently, in the degassing stage (o), the volatile components of the oopolymer mixture are removed in a degassing unit, the degassing unit comprising

at least one oopolymer mixture feeding hole,

at least one degassing device, the degassing device comprising

at least one degassing zone,

at least one gas outlet,

at least one copolymer melt outlet,

and at least one melt outlet die, wherein

the temperature of the copolymer melt Tv, °C in the last degassing zone, relative to the transport direction of the copolymer melt,

the temperature of the copolymer melt To, °C entering the melt outlet die and the total residence time t, s of the copolymer melt between the last degassing zone and the exit die of the melt of the degassing unit are adjusted in such a way that the term

is less than 8, preferably less than 6, even more preferably less than 4, particularly preferably less than 2.

The term "copolymer melt outlet", as used herein, refers to the outlet of the degassing device. In contrast, the term "melt outlet matrix" is the outlet of the entire degassing unit. After exiting the melt outlet die, the copolymer melt is typically cooled to a temperature of no more than 150°C, preferably less than 100°C, and granulated.

The copolymer melt temperature Tv, °C in the last degassing zone, is measured in the central part of the degassing zone. For practical reasons, the sensor measuring Tv is located no more than 10 mm, preferably no more than 5 mm above the polymer melt in the last degassing zone. The copolymer melt temperature To, °C is measured at the center of the inlet of the melt outlet die.

Steps (a) -(c) will be described below.

Polymerization stage (a)

Radical copolymerization of monomer mixtures comprising MMA and MAA is well known per se in the prior art. The polymerization step (a) may employ a method in which the polymerization is carried out in a state containing said mixture of monomers, a polymerization initiator and, optionally, a chain transfer agent and substantially not containing a solvent. (mass polymerization method). Alternatively, a solvent capable of dissolving the copolymer may be present or added during the polymerization (solution polymerization method). Polymerization can also be carried out in a dispersed medium, in which the monomers are dispersed in water or in an aqueous mixture.

In a preferred embodiment, the monomer mixture in step (a) comprises

from 80.0 to 99.5% by weight, preferably from 85.0 to 98.0% by weight of MMA;

from 0.5 to 20.0% by weight, preferably from 2.0 to 8.0% by weight, of the compound represented by formula (I)

the substituent R1 being a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms; and, optionally,

from 0.0 to 19.5% by weight, preferably from 0.0 to 7.0% by weight of a monomer selected from methyl acrylate, ethyl acrylate or styrene.

In the event that one or more of the optional monomers are present in the copolymer, typically the amount of the MMA monomer can be tailored accordingly.

Therefore, the resulting copolymer typically comprises

from 80.0 to 99.5% by weight, preferably from 85.0 to 98.0% by weight of repetitive units derived from MMA;

from 0.5 to 20.0% by weight, preferably from 2.0 to 8.0% by weight of repeating units derived from the compound represented by formula (I)

the substituent R1 being a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, preferably a methyl group; and, optionally,

from 0.0 to 19.5% by weight, preferably from 0.0 to 7.0% by weight of repeating units derived from methyl acrylate, ethyl acrylate or styrene.

In one embodiment, step (a) is carried out as a bulk polymerization, that is, without an added solvent. In a further embodiment, step (a) is carried out with a solvent, i.e. as a solution polymerization. If a solution polymerization method is employed, the solvent used in step (a) is not especially limited as long as it is capable of dissolving the copolymer at the polymerization temperature as described above and does not interfere with the polymerization procedure except some minor chain transfer. One or more solvents selected from aromatic hydrocarbons, ketones, ethers, esters, amides and alcohols may be used. Examples of a solvent that may be used include, but are not limited to, publicly known organic solvents, such as acetone, methyl ethyl ketone, methyl-n-butyl ketone, methyl isobutyl ketone, ethyl isobutyl ketone, tetrahydrofuran, dioxane, N,N -dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N -diethylacetamide, N-methyl pyrrolidone, propylene glycol, 2-methoxy-2-propanol and tetraglyme. In particular, solvents selected from toluene, butyl acetate, ethyl acetate, xylene, dimethylfuran or mixtures thereof are preferred.

If step (a) is carried out in a solvent, the solvent content in the reaction mixture typically ranges between 1.0% by weight and 60% by weight, more preferably between 5.0% by weight and 45% by weight. , based on the total weight of the reaction mixture.

The monomer mixture in the polymerization reactor may optionally comprise additional additives, selected from UV absorbers, UV stabilizers, lubricants, mold release agents, thermal stabilization agents, additives to increase scratch resistance, antistatic additives and colorants such as pigments or dyes. These additives will be described in detail later. The additives can be added to the polymerization reactor separately or as a mixture with MMA, with the compound represented by formula (I) or, if present, with methyl acrylate, ethyl acrylate or styrene.

It is further preferred that the oxygen concentration of the dissolved molecular air (O ² ) of the reaction mixture in the polymerization step (a) is controlled to be 70 ppm or less, so that the resulting copolymer has a Particularly low turbidity and yellowing index. To further inhibit coloration, the dissolved oxygen concentration is preferably less than 10 ppm. The dissolved oxygen concentration can be measured with a dissolved oxygen meter (for example, DO Meter B-505 as a galvanic oxygen sensor produced by lijima Denshi Kogyo KK).

The choice of a polymerization reactor for use in polymerization step (a) is not particularly limited. The polymerization reactor may comprise or be a batch- or continuously-operated stirred tank reactor, a continuously-operated tubular reactor, a batch- or continuously-operated loop reactor, or a combination of any of these, and where if several reactors are used, they can be operated in parallel or can be connected sequentially.

The monomers can be added to the reactor as a mixture or as separate feeds. The polymerization step (a) can be carried out in a batch reactor or a semi-continuous type of reactor, in which the initiator, if present, the solvent, the monomer or a combination of any of them it feeds optionally during the polymerization step (a). Alternatively, the polymerization step (a) can be carried out in a continuous polymerization process such as in stirred tank reactors (CSTR), in a tubular reactor or a combination thereof, in kneaders or in reactors. of disc ring.

In some embodiments, the copolymer reaction mixture from the outlet of the first CSTR can be successively supplied continuously to a second and/or third reaction device, for example, another CSTR or to a tubular reactor to increase the conversion. The term "conversion", as used in the present application, refers to an average weight ratio of the copolymer formed in polymerization step (a) to the total monomer feed.

The conversion rate can be easily adjusted by an expert by adapting the average residence time of the reaction mixture in the reactor, the polymerization temperature, the reactivity of the initiator used and the amount of initiator and the concentration of monomer in the reactor feed. . For example, if a CSTR is used, the mean residence time is preferably selected in the range of 10 minutes to 7 hours, more preferably 20 minutes to 6 hours, for example 30 minutes to 4 hours. Average residence times greater than 7 hours are generally disadvantageous in terms of productivity and profitability.

The polymerization temperature during polymerization step (a) in a CSTR is advantageously maintained in a range of 60°C to 200°C, more preferably 70°C to 180°C, particularly preferably 80°C to 170 °C to avoid an excessive increase in the viscosity of the reaction mixture in the reactor. It is preferred that the conversion of monomers at the outlet of the CSTR be maintained in a range of 30 to 70% by weight, based on the total weight of monomers added to the reaction mixture. If the polymer blend output of the above-described CSTR is fed to a second CSTR, the conversion of the second CSTR is preferably kept in the range of 30% by weight to 80% by weight.

In a further embodiment, the polymerization step (a) can be carried out in a tubular type reactor. Both bulk polymerization and solution polymerization can be carried out continuously in a tubular reactor with or without mixing elements. It is preferred that the conversion of monomers at the outlet of the tubular reactor be maintained in a range of 50 to 98% by weight, based on the total weight of monomers added to the reaction mixture. With a conversion below 50% by weight, the process becomes economically disadvantageous. On the other hand, the conversion should not exceed 98% by weight, since it unnecessarily increases the average residence time in the tubular reactor. An even more preferred range is 55 to 96% by weight, and a more preferred range is 60 to 94% by weight, in particular, if the tubular reactor is operated in combination with another reactor and is the final polymerization reactor used. in the polymerization stage (a).

The average residence time of the reaction mixture in the tubular reactor is not particularly limited. For practical reasons, it is commonly kept within a range of 20 s to 8 hours. If the average dwell time is less than 20 s, the conversion is still low. On the other hand, the average residence time in a tubular reactor should not exceed 9 hours, for productivity reasons.

As a method of adding the radical polymerization initiator in the tubular reactor, it is preferred to add the radical polymerization initiator together with the feed of the monomers and/or the solvent. Equally preferred is a method of preliminarily mixing the radical polymerization initiator in a static mixer arranged in series at the inlet of the tubular reactor and passing the mixture through said tubular reactor. Furthermore, it is possible and advantageous to add at least some of the monomers and/or the solvent and/or the same or a different type of initiator, downstream along the tubular reactor, to ensure even better control of the conversion during the reaction. polymerization stage (a) and the composition of the copolymer formed.

Furthermore, for improved adjustment of the temperature rise of the reaction mixture, it is preferred to add the radical polymerization initiator at a location immediately upstream of the reaction mixture inlet of the tubular reactor and optionally at one or more locations. inside the reactor. This allows the polymerization to proceed more efficiently.

The copolymer content in the reaction mixture in a tubular reactor can normally be maintained in a range of 50 to 98% by weight, more preferably 60 to 96% by weight, even more preferably 60 to 94% by weight to ensure an efficient polymerization.

It is advantageous to use a radical polymerization initiator with a half-life of 0.05 to 90 minutes in a CSTR at the polymerization temperature. A more preferred range is 0.05 to 60 minutes, and the most preferred range is 0.1 to 20 minutes. If the decomposition half-life is less than 0.05 minutes, since the radical polymerization initiator decomposes before it is uniformly dispersed in the polymerization reactor, the efficiency (initiation efficiency) of the polymerization initiator in radicals it decreases. If the amount of radical polymerization initiator is increased, the heat resistance of the resulting copolymer decreases. On the other hand, if the decomposition half-life is more than 90 minutes in CSTR, it is difficult for the polymerization to work stably. Furthermore, the concentration of initiator in the CSTR accumulates when the decomposition half-life is high, which can sometimes lead to unsafe situations, since the polymerization and the heat of polymerization generated can hardly be controlled. This can lead to a runaway of the polymerization temperature in the CSTR.

Furthermore, when the polymerization is additionally performed in the tubular reactor, it is preferred to add one or more radical polymerization initiators with a decomposition half-life of 0.1 to 8 hours at the reaction temperature of the tubular reactor. A more preferred range is 1 to 7 hours. It is not preferred that the decomposition half-life of radical polymerization initiators be greater than 8 hours, since it is difficult to control the polymerization. On the other hand, it is not preferred that the decomposition half-life be too short, because the radical polymerization initiator will decompose quickly, not allowing the conversion to increase sufficiently. As a consequence, a copolymer with poor heat resistance would be produced. Therefore, it is preferred to use a radical polymerization initiator with a decomposition half-life of 0.1 hour or greater.

One radical polymerization initiator can be used or two or more can also be used as a mixture. In the case where two or more radical polymerization initiators are used in the tubular reactor, it is preferred to use different radical polymerization initiators in the half-life of 10 hours of decomposition temperature at 5 °C or more . This allows the polymerization in step (a) to proceed more efficiently.

The radical polymerization initiator can be selected, for example, from organic peroxides such as ferc-butyl peroxy-3,5,5-trimethylhexanoate, ferc-butyl peroxy laurate, ferc-butyl peroxy isopropyl monocarbonate. butyl, peroxyhexyl ferc.-butyl monocarbonate, peroxy ferc.-butyl acetate, 1,1-bis(ferc.-butyl peroxy)-3,3,5-trimethylcyclohexane, 1,1-bis(ferc.-butyl peroxy)cyclohexane, peroxy ferc.-butyl 2-ethylhexanoate, peroxy ferc.-butyl isobutyrate, peroxy ferc.-hexyl 2-ethylhexanoate, di-ferc.-butyl peroxide, 2,5-dimethyl-2,5 -bis(ferc.-butyl peroxy)hexane, lauroyl peroxide, benzoyl peroxide, ferc.-butyl peroxy neodecanoate, ferc.-butyl peroxy pivalate, ferc.-butyl peroxy-2-ethylhexanoate, ferc.-butyl peroxy benzoate .-butyl and dicumyl peroxide, azo compounds, such as 2-(carbamoylazo)-isobutyronitrile, 1,1'-azobis(1-cyclohexanecarbonitrile), 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile ), dimethyl 2,2'-azobisisobutyrate, 2,2'-azobis(2,4,4-trimethylpentane), 2,2'-azobis(2-methylpropane), 2,2'-azobis-4-methoxy- 2,4-dimethylvaleronitrile and 2,2'-azobis-2,4-dimethylvaleronitrile, and the like.

The amount of radical polymerization initiator used in polymerization step (a) is adjusted depending on the polymerization temperature, the polymerization time (average retention time) and the intended conversion rate. It is preferred that the amount be 0.001 to 2.0% by weight, based on the total weight of the reaction mixture in polymerization step (a). A more preferred range is 0.01 to 2.0% by weight, and an even more preferred range is 0.01 to 1.0% by weight.

In order to control the molecular weight of the copolymer, it is often advantageous to add from 0.001 to 2.0% by weight, more preferably from 0.005 to 2.0% by weight, and even more preferably from 0.01 to 1.0 % by weight, based on the total weight of the reaction mixture in polymerization step (a), of a chain transfer agent. Suitable chain transfer agents per se are well known in the prior art and can be selected, e.g. e.g., of an alkyl mercaptan, carbon tetrachloride, carbon tetrabromide, dimethylacetamide, etc. Examples of an alkyl mercaptan used in polymerization step (a) include, infer alia n-octyl mercaptan, ferc.-dodecyl mercaptan, n-dodecyl mercaptan, n-tetradecyl mercaptan, n-octadecyl mercaptan, etc. Among them, n-octyl mercaptan, n-dodecyl mercaptan and methyl mercaptopropionate can be used advantageously.

In a preferred embodiment, the copolymer mixture obtained in a CSTR is successively supplied continuously to a tubular reactor to carry out further polymerization. This reduces the amount of volatile components that must be removed at a later stage, making the entire procedure even more cost-effective.

The method of supplying the copolymer mixture obtained in the CSTR to a second reactor, for example, a second CSTR, a tubular reactor or a tubular loop reactor, is not especially limited. For example, the operation of removing the reaction mixture from the first CSTR to the second reactor can be performed using a pump. As a liquid feed pump, a publicly known gear pump can be suitably used. If the reaction mixture is removed by a pump, the reaction mixture can be stably fed to the second reactor, and the pressure in the second reactor, which optionally has static mixing structure portions installed in succession, can rise above the vapor pressure of the reaction mixture. As a further possibility, the reaction mixture can be transferred from the CSTR to a second reactor by means of the pressure difference between the reactors.

The total conversion in polymerization step (a) is usually at least 40% by weight, more preferably at least 45% by weight. Conversion less than 40% by weight is disadvantageous for economic reasons. On the other hand, it is not preferred that the final conversion be greater than 98% by weight, since the polymerization time becomes too long for economic reasons. A preferred range is 40 to 96% by weight, and a more preferred range is 45 to 94% by weight.

Heating stage (b)

According to the present invention, the copolymer mixture obtained in the polymerization step (a) can be supplied to an optional step of heating the copolymer mixture to a temperature of 100 ° C to 300 ° C (heating step ( b)). This can be done advantageously using a heat exchanger. The design of the heat exchanger is not particularly limited. The heat exchanger can be e.g. e.g., a tubular bundle of tubes arranged in parallel. Alternatively, a heat exchanger may be a plate heat exchanger.

The heat exchanger may optionally contain static mixing elements or an agitator. Examples of static mixing elements include Sulzer type SMX and type SMR tubular mixers, Kenics static mixers, Toray tubular mixers, etc. Alternatively, the heat exchanger may not contain mixing elements.

Heating of the copolymer mixture can optionally be carried out using a jacket filled with hot oil, water, steam and/or, alternatively, using electrical heating elements.

Degassing stage (c)

After the polymerization step (a) or after the optional heating step (b), the copolymer mixture is subsequently supplied to a degassing unit for the degassing step (c), in which the volatile components, such as monomers that have not reacted, methanol and, if present, the solvents are removed. Stage (c) is carried out in a degassing unit that comprises at least one feed orifice of the copolymer mixture, at least one degassing device and at least one melt outlet. The degassing device comprises at least one degassing zone, at least one gas outlet and at least one copolymer melt outlet. Furthermore, as a person skilled in the art will readily appreciate, the degassing unit may comprise additional elements, such as, for example, ducts, melt filters, etc. located between the degassing device and the melt outlet matrix. For example, to minimize contamination of the copolymer with solid foreign matter, the degassing unit used in the degassing step (c) may optionally comprise at least one melt filter, located between the last degassing zone of the degassing device, relative to the transport direction of the copolymer melt and the melt outlet matrix.

Melt filters are usually devices installed in the copolymer melt flow in a melt conduit and are equipped with mesh screens. Mesh sieves can be made of stainless steel and typically include several connected sieve layers. Melt filters are designed in such a way that they can remove small solid contaminations from the copolymer melt. For continuous operation, it is more advantageous to use a self-cleaning melt filter which is also called a double piston screen changer, e.g. e.g., a RSFGENIUS series melt filter, commercially available from Gneuss or a KSWE series melt filter, commercially available from Nordson-BKG. A melt filter with installed melt sieves typically has a holding volume that is filled with the flowing copolymer melt. The retention of the melt filter contributes to the residence time t of the copolymer melt after the last degassing zone.

The temperature of the copolymer mixture in the degassing step is typically less than 300°C, more preferably 150°C to 300°C, even more preferably 170°C to 290°C. The preferred pressure in the last degassing zone of the degassing step is an absolute pressure, typically below 500 mbar, more preferably below 300 mbar. The lower limit of the absolute pressure in the degassing stage is not limited, but for technical reasons it is normally at least 1 mbar or more. For example, the absolute pressure in the last degassing zone of the degassing device, relative to the transport direction of the copolymer melt, can advantageously be set in the range of 1 mbar to 300 mbar, preferably from 10 mbar to 200 mbar, or between 1 mbar and 300 mbar, preferably between 10 mbar and 200 mbar.

If the pressure in the degassing step is greater than 500 mbar, even if the devolatilization is carried out within said temperature range, typically the unreacted monomers or the mixture consisting of the unreacted monomers and the solvent of polymerization, if present, cannot be separated or removed efficiently. This is disadvantageous in terms of heat resistance and mechanical and optical properties of the resulting copolymer.

The degassing device in the degassing step (c) is not particularly limited and can be selected from a degassing extruder, a degassing kneader and one or more static instantaneous chambers. In particular, a single screw degassing extruder or a twin screw degassing extruder, a static flash chamber, a degassing kneader or a combination thereof may be advantageously used. One embodiment is an apparatus that has a cylindrical vessel and a stirrer that has multiple stirring elements fixed to a rotating shaft and has at least one or more degassing holes in the top of the cylindrical part, a mixture feed hole of copolymers to supply the copolymer mixture at one end of the cylindrical portion and a melt outlet of oopolymers to remove the oopolymer melt after completing devolatilization at the other end. The number of rotating axes is not limited, but is usually 1 to 5, preferably 1 or 2, and an apparatus having two rotating axes is more preferred. In particular, a ventilated continuous one or two screw extruder (kneading apparatus, and batch type melt kneading apparatus) is preferred, and single screw extruder, twin screw extruder, kneading extruder may be mentioned here. combined twin screw/single screw continuous, and triple screw extruder respectively with “Unimelt” type screw or screws, and continuous or batch type kneading machine. Above all, a single- or two-screw ventilated extruder, or a continuous twin-screw reactor with multiple blades of elliptical and/or convex lens type plates, can preferably be used.

Furthermore, the degassing step (c) in the production process of this invention may employ a method of using two or more devolatilization apparatus arranged in series to perform devolatilization, and this is advantageous, since the remaining volatile component in The copolymer melt obtained after devolatilization can be reduced even further.

After leaving the degassing device of the degassing unit, the material normally passes through other elements such as melt conduits, melt filters, etc. and finally exits the degassing unit through the melt outlet die.

According to the present invention,

the temperature of the copolymer melt Tv, °C (T ^v given in eO) in the last degassing zone, relative to the transport direction of the copolymer melt,

the temperature of the copolymer melt To, °C (To given in °C) entering the melt outlet die and

The total residence time t, s (t expressed in s) of the copolymer melt between the last degassing zone and the melt outlet matrix of the degassing unit are adjusted such that the term

is less than 8, preferably less than 6, even more preferably less than 4, particularly preferably less than 2. The temperature of the copolymer melt Tv, °C in the last degassing zone, is measured in the central part of the degassing zone. The copolymer melt temperature To, °C is measured at the center of the inlet of the melt outlet die. Importantly, by keeping the above term below 8, preferably below 6, even more preferably below 4, particularly preferably below 2, the unwanted formation of glutaric anhydride units in the polymer chain can be efficiently suppressed so that the copolymer exiting the melt exit die has a high content of free carboxylic acid functionalities. After exiting the melt outlet die, the copolymer melt typically undergoes rapid cooling and granulation. This also ensures a high content of free carboxylic acid functionalities.

Despite the above, the inventors found that the unwanted formation of glutaric anhydride units can be suppressed even further if the temperature of the copolymer melt Tv, °C in the last degassing zone and the temperature of copolymer melt To, °C upon entering the melt outlet die are adjusted in such a way that the term (1.5 . Tv + 0.5 ■ To) / 2), is maintained in the range of 230 to 290 °C or between 230 °C and 290 °C. Often, at temperatures above 290 °C, the formation of glutaric anhydride units leads to a significant consumption of carboxylic acid functionalities in the copolymer, accompanied by the formation of methanol and water. As a consequence, the adhesive properties of the copolymer on metal or ceramic surfaces are compromised to some extent. On the other hand, at melting temperatures below 230 °C, it was often found that the devolatilization rate of the copolymer was insufficient and that the copolymer melt exiting the melt exit die contained higher amounts of volatile organic compounds. This has a negative impact on the heat resistance of the final product.

The time t of the copolymer melt between the last degassing zone and the melt outlet die of the degassing unit can be adjusted by adapting the length of the melt conduits and the number of optional elements, such as such as melt filters, melt sieves, etc. Lower residence times t generally lead to the suppression of unwanted formation of glutaric anhydride units and are therefore advantageous. For practical reasons, the residence time t, s of the copolymer melt between the last degassing zone, relative to the transport direction of the copolymer melt, and the melt outlet die is typically adapted so that it is in the interval between 10 s and 200 s or in the interval between 10 s and 200 s. The melt outlet matrix usually has a volume relatively small retention chamber filled with the polymer melt. The melt outlet die may optionally have a jacket that can be heated or cooled.

To further minimize the formation of glutaric anhydride units, it is preferred that after exiting the melt outlet die, the final copolymer melt undergoes solidification and granulation in no more than 10 s, preferably no more than 5s. The term "solidification", as used herein, refers to cooling to a temperature of no more than 150°C, preferably less than 100°C.

Molding composition

In its further aspect, the present invention relates to a molding composition obtainable by (or obtained by) the process described above. The molding composition comprises at least 80% by weight, preferably at least 90% by weight of a copolymer, said copolymer comprising

from 80.0 to 99.9% by weight, preferably from 85.0 to 98.0% by weight of repetitive units derived from MMA; and

from 0.1 to 20.0% by weight, preferably from 2.0 to 15.0% by weight, also preferably from 2.0 to 8.0% by weight of repeating units derived from the compound represented by the formula (I )

the substituent R1 being a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, preferably methyl,

optionally, from 0.0 to 19.9% by weight, preferably from 0.0 to 7.0% by weight of repeating units derived from methyl acrylate, ethyl acrylate or styrene; and

no more than 2.5% by weight, preferably no more than 2.0% by weight of repeating units represented by formula (II)

the substituents R2 and R3 being independently a hydrogen atom or a hydrocarbon group of 1 to 6 carbon atoms, preferably both being represented by a methyl group.

In case one or more optional repeating units are present in the copolymer, typically the amount of MMA-derived repeating units can be tailored accordingly.

As explained above, the process of the present invention effectively suppresses the unwanted intramolecular cyclization reaction that forms glutaric anhydride units represented by formula (II) from MAA units in the copolymer. As a consequence, the formation of methanol and water as byproducts during degassing of the copolymer melt is also suppressed. Furthermore, under the preferred degassing conditions, unreacted monomers, such as MMA and MAA, can be effectively removed and therefore their concentration in the final copolymer is also low. Therefore, the copolymer melt exiting the melt outlet die of the degassing unit has a particularly low content of volatile compounds. Materials of this type are not accessible using prior art procedures.

In particular, the molding composition may contain an amount as low as less than 1400 ppm, preferably no more than 1000 ppm of methanol, based on the total weight of the molding composition.

It is also advantageous that the molding composition comprises no more than 1800 ppm, preferably no more than 1500 ppm of MAA, based on the total weight of the molding composition. Furthermore, the molding composition of the present invention should advantageously comprise no more than 5000 ppm, preferably no more than 4000 ppm of MMA, based on the total weight of the molding composition.

The mass average molecular weight Mw of the copolymer is not particularly limited and is typically about 40,000 to 500,000 g/mol, more preferably 60,000 to 400,000 g/mol. The number average molecular weight Mn of the copolymer is preferably 20,000 to 150,000 g/mol, more preferably 25,000 to 100,000 g/mol. The determination of M ^w and Mn can be carried out, e.g. e.g., by gel permeation chromatography (GPC), for example using PMMA as calibration standard and tetrahydrofuran (THF) with 0.2% by volume trifluoroacetic acid (TFA) as eluent. As an alternative to using a calibration standard, a dispersion detector can also be used for copolymers having an M ^w of more than 100,000 g/mol ( see HF Mark et al., Encyclopaedia of Polymer Science and Engineering, 2nd Edition, Vol. 10, page 1 et seq., J. Wiley, 1989). Appropriate GPC columns can be easily selected by an expert, for example HPS columns. Columns of this type are commercially available, for example, from PSS Standards Service GmbH (Mainz, Germany) as PSS SDV series columns. As will be easily appreciated, a combination of several GPC columns can also be used.

Due to the decrease in cyclization of the MAA units in step (c) of the procedure, the weight ratio of the repeating units represented by formula (II)

to the weight of the repeating units derived from the compound represented by formula (I)

in the copolymer it is below 0.2, preferably below 0.1.

Additional additives

The molding composition of the present invention may further contain at least one common polymer additive as long as the latter does not adversely affect the optical and adhesive properties of the copolymer of the present invention. Various polymeric additives are well known to a person skilled in the art and include, inter alia, impact modifiers, UV absorbers, UV stabilizers, light stabilizers, antioxidants, colorants, flow improvers, pigments, flame retardants, lubricants and processing aids. release agents, dispersant particles, aids to improve scratching, thermal stabilizers, antistatic additives, additives to increase scratch resistance, etc. The heat resistance of the resulting molding composition should not be unduly affected by these additives.

Additives can be added at any stage of the manufacturing procedure as long as their presence does not interfere with the procedure. For example, during the polymerization step (a) additives such as UV absorbers, lubricants, mold release aids and colorants, such as pigments or dyes, are often added to the reaction vessel, together with the monomers or separately. As a further possibility, these additives can be added to the copolymer melt in or after the degassing device in degassing step (c).

UV absorbers and UV stabilizers

UV absorbers and UV stabilizers and light stabilizers for use in the present invention are well known and are described in detail by way of example in Hans Zweifel, Plastics Additives Handbook, Hanser Verlag, 5S edition, 2001, p. . 141 et seq. UV stabilizers are understood to include UV stabilizers and free radical scavengers. Free radical scavengers are, for example, spherically hindered phenols such as, without restriction, octadecyl-3-[3,5-di-tert-butyl-4-hydroxyphenyljpropionatoj, tetrakis[3-[3,5-di-tert, - pentaerythritol butyl-4-hydroxyphenylpropionate and salicylic esters. UV absorbers can be derived, e.g. e.g., from the group of substituted benzophenones, salicylic esters, cinnamic esters, oxanilides, benzoxazinones, hydroxyphenylbenzotriazoles, benzotriazoles, triazines, or benzylidenemalonate. An example of hydroxyphenyl benzotriazole is 2-(2H-benzotriazol-2-yl)-p-cresol, sold as Tinuvin® P or Drometrizol, tetraethyl-2,2'-(1,4-phenylenedimethylidin)bismalonate, sold as Hostavin® B-CAP, n-(2-ethoxyphenyl)-n'-(4-ethylphenyl)-ethylenediamide sold as Tinuvin® 312. The total content of UV absorbers in the molding composition typically ranges from 0.01% by weight to 1.0% by weight, especially from 0.01% by weight to 0.5% by weight, in particular from 0.02% by weight to 0.2% by weight, based on the weight of the molding composition .

UV absorbers may be present in the molding composition as low molecular weight compounds. However, the UV-absorbing groups on the matrix copolymer molecules can also be covalently linked after copolymerization with polymerizable UV-absorbing compounds, such as, for example, acrylic, methacrylic or allylic derivatives of benzophenone derivatives or derivatives of benzotriazole. As a skilled person will readily appreciate, mixtures of chemically different UV absorbers can also be used, e.g. e.g., benzotriazoles in combination with triazines.

The best-known representatives of UV stabilizers/free radical scavengers are provided by the hydroxyphenyl benzotriazole group or spherically hindered amines (hindered amine type light stabilizer, HALS). Examples of suitable free radical scavengers/UV stabilizers include, inter alia , spherically hindered phenols and spherically hindered amines, which are known as HALS (Spherically Hindered Amine Type Light Stabilizer). Tetramethylpiperidine present in HALS compounds is responsible for their stabilizing effect. This class of compounds may be unsubstituted or substituted with alkyl or acyl groups on the piperidine nitrogen. Spherically hindered amines do not absorb in the UV range. They trap free radicals formed, which again UV absorbers are incapable of doing. Free radical scavengers/UV stabilizers are used in the compositions according to the invention in amounts of 0.01% by weight to 1.5% by weight, especially in amounts of 0.02% by weight to 1.0% by weight, in particular, in amounts of 0.02% by weight to 0.5% by weight, based on the weight of the molding composition. A combination of UV stabilizers/absorbers, light stabilizers and antioxidants is also possible.

Thermal processing color stabilizers

Suitable thermal processing color stabilizers are not particularly limited and can be selected from, e.g. e.g., triphenyl phosphates, tris-(2,4-di-tert-butylphenyl)-phosphate, tris-(2,5-di-tert-butylphenyl)-phosphate, triphenyl phosphites or tris-(2, 4-di-tert.-butylphenyl)-phosphite.

Dispersion particles

In some embodiments of the present invention, the molding composition may further comprise organic or inorganic dispersion particles dispersed in the polymer matrix. Although the choice of dispersion particles is not particularly limited, they are typically selected such that the refractive index of the dispersion particles differs from that of the copolymer matrix by at least 0.01. The refractive index can be measured on the D line of Na at 589 nm at 23 °C as specified in ISO 489 (1999).

The dispersion particles typically have a weight average particle diameter of 0.1 gm to 100.0 gm. The weight average particle diameter - indicated as the so-called volume average d50 value (i.e. 50 vol % of the particles have a particle size below the specified average particle size) of the dispersion particles is can measure according to the standard for laser diffraction measurements ISO 13320-1 (2009). Typically, the size of the dispersion particles is determined in each case in dry powder form by laser light scattering (at room temperature, 23 °C) using the Beckman Coulter LS 13320 laser diffraction particle size analyzer, dry dust tornado. The measurement is carried out as described in the manual. For computer-assisted analysis, the Mie model is used.

Inorganic dispersion particles may include traditional inorganic opacifiers, e.g. e.g., barium sulfate, calcium carbonate, titanium dioxide or zinc oxide.

Organic dispersion particles are typically spherical dispersion beads consisting of a cross-linked polymeric material, such as alkyl poly(meth)acrylates, silicones, polystyrenes, etc. For the purposes of the present invention, the term "spherical" means that the dispersion beads preferably have a spherical shape, but it is clear to the skilled person that, as a consequence of the production methods, it is also possible that dispersion beads are present. dispersion with some other shape, or that the shape of the dispersion beads may deviate from the ideal spherical shape. Therefore, the term "spherical" indicates that the ratio between the largest dimension of the dispersion beads and the smallest dimension is not greater than 4, preferably not greater than 2, and each of these dimensions is measured across the center of gravity of the scattering beads. Based on the number of dispersion beads, preferably at least 70% are spherical, particularly at least 90%.

Preferred dispersion beads composed of cross-linked polystyrenes are commercially available from Sekisui Plastics Co., Ltd. under the trademarks Techpolymer® SBX-4, Techpolymer® SBX-6, Techpolymer® SBX-8 and Techpolymer® SBX-12.

Other particularly preferred spherical plastic particles used as dispersing agents comprise cross-linked silicones. Silicone dispersing agents particularly preferably used in the present invention can be obtained from Momentive Performance Materials Inc. as TOSPEARL® 120 and TOSPEARL® 3120.

Impact modifiers

Mechanical properties of the molding composition can be further tailored to the desired purpose if the thermoplastic copolymer comprises an impact modifier. Impact modifiers for use in the present invention per se are well known and can have different chemical compositions and different copolymer architectures. Impact modifiers can be cross-linked or thermoplastic. Additionally, the impact modifiers may be in particulate form, such as core-shell or core-shell-shell particles. Typically, particulate impact modifiers have an average particle diameter between 20 nm and 500 nm, preferably between 50 nm and 450 nm, more preferably between 100 nm and 400 nm and most preferably between 150 nm and 350 nm. "Particulate impact modifiers" in this context means cross-linked impact modifiers that generally have a core, core-shell, core-shell-shell, or core-shell-shell-shell structure. The average particle diameter of the particulate impact modifiers can be determined by a method known to a skilled person, e.g. e.g. by photon correlation spectroscopy in accordance with DIN ISO 13321: 1996.

In the simplest case, the particulate impact modifiers are cross-linked particles obtained by emulsion polymerization, whose average particle diameter is in the range of 10 nm to 150 nm, preferably 20 nm to 100 nm, more preferably 30 nm. at 90nm. These are generally composed of at least 20.0% by weight, preferably from 20.0% by weight to 99.0% by weight, particularly preferably in the range of 30.0% by weight to 98.0% by weight of butyl acrylate, and from 0.1% by weight to 2.0% by weight, preferably from 0.5% by weight to 1.0% by weight of a cross-linking monomer, e.g. e.g., a polyfunctional (meth)acrylate, e.g. allyl methacrylate and, if necessary, other monomers, e.g. e.g., from 0.0% by weight to 10.0% by weight, preferably from 0.5% by weight to 5.0% by weight, of C1-C4 alkyl methacrylates, such as ethyl acrylate or butyl methacrylate, preferably methyl acrylate or other polymerizable vinyl monomers, e.g. e.g., styrene.

A three-layer or triphasic structure with a core and two shells can be prepared as follows. The innermost (hard) core may be composed of, for example, MMA, small proportions of comonomers, e.g. e.g., ethyl acrylate, and a proportion of cross-linking agent, e.g. e.g., allyl methacrylate. The middle (soft) shell may be composed, for example, of a copolymer comprising butyl acrylate and, if applicable, styrene, while the outermost (hard) shell is the same as the polymer matrix, providing compatibility and good union with the matrix. The proportion of poly(butyl acrylate) in the core or shell of the impact modifier of a two- or three-layer core-shell structure is decisive for the impact-modifying action and is preferably in the range of 20. 0% by weight to 99.0% by weight, particularly preferably in the range of 30.0% by weight to 98.0% by weight, even more preferably in the range of 40.0% by weight to 97, 0% by weight, based on the total weight of the impact modifier.

Thermoplastic impact modifiers have a different mechanism of action than particulate impact modifiers. They are generally mixed with the matrix material. In the case where domains are formed, as occurs, for example, in the case of the use of block copolymers, the preferred sizes for these domains, the size of which can be determined, for example, by electron microscopy, correspond to preferred sizes for the core-shell particles.

A further class of thermoplastic polymers for use in accordance with the present invention as impact modifiers are methacrylate-acrylate block copolymers, especially acrylic TPE, comprising PMMA-n-butyl poly-acrylate-PMMA triblock copolymers, and that are commercially available, e.g. e.g., under the product name Kurarity® by Kuraray. The poly-n-butyl acrylate blocks form nanodomains in the copolymer matrix that are between 10 nm and 20 nm in size.

Lubricants and mold release agents that can reduce or completely prevent possible adhesion of the molding composition to the injection mold are important for the injection molding process, and may also be employed. For example, they may be present as auxiliaries, lubricants, selected from the group consisting of saturated fatty acids, esters or inorganic salts having less than C ²⁰ , preferably C ¹⁶ to C ¹⁸ , carbon atoms, or in saturated fatty alcohols having less than C ²⁰ , preferably C ¹⁶ to C ¹⁸ , carbon atoms. For example, stearic acid, stearyl alcohol, palmitic acid, palmitic alcohol, lauric acid, lactic acid, glycerol monostearate, pentaerythrol, and industrial mixtures of stearic and palmitic acid. Also n-hexadecanol, n-octadecanol and industrial mixtures of n-hexadecanol and n-octadecanol and glycerol monostearate are suitable. A particularly preferred lubricant or mold release agent is stearyl alcohol. Lubricants are typically used in amounts of no more than 1.0% by weight, e.g. e.g., from 0.05% by weight to 0.25% by weight based on the weight of the molding composition.

Flow improvers may optionally be used to reduce the melt viscosity of the copolymer composition. Typically they usually consist of oligomers or may be selected from the group consisting of saturated fatty acids, esters or inorganic salts preferably having C16 carbon atoms or more of the saturated fatty alcohols or fatty acids, polyethylene glycols and glycerol monostearate. Flow improvers are typically used in amounts of no more than 5.0% by weight, e.g. e.g., from 0.5% by weight to 4.0% by weight based on the weight of the molding composition.

The molding composition herein can optionally be colored in various colors using soluble organic dyes. Typically, perinone, azo and anthraquinone type dyes are used for this purpose due to their commercial availability and bright colors. The term "soluble", as used in the present application, indicates that the colorant is soluble in the matrix of the thermoplastic copolymer in amounts in which it is used to color the same. Accordingly, a colored molding composition is a thermoplastic composition comprising an organic colorant that is uniformly distributed in the thermoplastic polymer matrix.

The molding composition of the present invention has excellent transparency and a clear, substantially non-cloudy appearance. In particular, the haze of the molding composition, measured at 232C in an injection molded specimen having a thickness of 3.0 mm according to ASTM D1003 (2013), is usually less than 5%, preferably less than 3%. , more preferably less than 2%, especially preferably less than 1%.

Furthermore, the molding composition without color additives or coloring pigments preferably shows a light transmittance, T ^d65 , according to DIN 5033-7 (2014), in the range of 85% to 93%, more preferably in the range of 87%. at 92%, measured at 232C in an injection molded specimen having a thickness of 3.0 mm.

The yellowing index of the molding composition without coloring additives or coloring pigments, determinable according to DIN 6167 (1980) (illuminant D65, 102 in a layer thickness of 3.0 mm), should preferably be less than 7, preferably less than 5 , measured at 232C in an injection molded specimen having a thickness of 3.0 mm, in the absence of added dyes or pigments.

Advantageously, the Vicat softening temperature of the molding composition according to ISO 306-B50 (2014) is at least 105°C, preferably at least 110°C, more preferably at least 115°C. The nominal elongation at break of the molding composition without impact modifier according to ISO 527 (2012) should preferably be at least 2.0%, particularly preferably 2.5% or higher.

The modulus of elasticity of the molding composition according to ISO 527 (2012) is advantageously greater than 3000 MPa, preferably greater than 3500 MPa, if no impact modifier is present.

Due to its advantageous rheological properties, the molding composition of the present invention is very suitable for the manufacture of optical elements by injection molding. The composition of the present invention typically has a melt volumetric flow rate MVR measured in accordance with ISO 1133 (2012) at 230 ° C and 3.8 kg, greater than 0.2 cm3 / 10 min, preferably greater than 0.4 cm3 / 10 min, most preferably in the range of 0.6 cm3 / 10 min to 15.0 cm3 / 10 min.

The molding composition of the present invention can be thermoplastically processed by common methods such as injection molding and extrusion to give molded articles. Injection molding of the composition can be carried out in a known manner at temperatures in the range of 200°C to 300°C (melting temperature) and a mold temperature of preferably 60°C to 120°C. The extrusion is preferably carried out at a temperature of 200°C to 280°C.

Due to its high heat resistance, low haze and a high content of free carboxylic acid groups, the molding composition and the molded article manufactured therefrom are well suited for optical applications with acrylic elements tightly bonded to metallic structural elements or ceramics. For example, applications of this type include optoelectronic devices, preferably light emitting diodes, optical sensors or solar cells; optical elements; optical lenses; light guides; lamp covers, preferably for room lighting systems or automobile lighting equipment, black pillar trims; car light covers The molding composition of the invention can also be used advantageously in displays for communication devices, especially PDAs, mobile phones, preferably smartphones; tablets; TV devices; kitchen appliances, street lights and other electronic devices.

The following examples illustrate the invention in detail. However, it is not intended that the present invention be limited to these examples.

Examples

Analysis

GPC measurement conditions

Product properties

Specimens of 3.0 mm thickness were prepared by injection molding at 250 ^s C, and subsequently stored for 72 h at 23 s C and 50% relative humidity before measurements.

Turbidity was determined using a BYK Gardner Hazegard-plus turbidimeter in accordance with ASTM D 1003 (1997).

The Vicat VST ISO 306-B50 (2014) softening temperature was measured using 3.0 mm thick specimens that were stored for 16 h at 100 °C before measurements.

Copolymer composition

Determination of methanol residues in the final copolymer

Calibration method: external standard

Preparation of copolymer solution for analysis:

1000 mg of the copolymer was weighed into an Erlenmeyer flask and 20 ml of N,N-dimethylformamide (DMF) was added. The sample was dissolved overnight by stirring and the methanol content was determined by gas chromatography (GC).

Determination of MMA residues in the final copolymer

Calibration method: external standard

Preparation of copolymer solution for analysis:

1000 mg of the copolymer was weighed into an Erlenmeyer flask and 20 ml of DMF was added. The sample was dissolved overnight by stirring, and the content of MMA residues was determined by GC.

GC Analysis on a Headspace Gas Chromatograph

The calculation of the content was carried out with software, based on the calibration constants.

Determination of MAA residues in the final copolymer

Calibration method: external standard

Preparation of copolymer solution for analysis:

2 g of the copolymer was dissolved in 50 ml of acetone and 5 ml of this solution was poured into 20 ml of a 70:30 methanol/water mixture. 5 ml of that solution was poured into 20 ml of ultrapure water and the content of MAA residues were determined by high-performance liquid chromatography (HPLC),

HPLC Analysis with an Agilent HPLC Device

The calculation of the content was carried out on the basis of a peak area with software, based on the calibration constants, Determination of MAA units and glutaric anhydride units in the final copolymer.

A two-stage analysis with a hydrolysis step was carried out as follows:

Titration before hydrolysis:

0.5 g of the copolymer was dissolved in 80 ml of pyridine at 50 °C and the solution was titrated,

Each measurement was accompanied by two blank feed measurements (same procedure, but without the copolymer sample),

Titration after hydrolysis:

0.5 g of the copolymer was dissolved in 40 ml of pyridine at 500C. 15 ml of demineralized water was added and kept at 98 °C for 2 h for hydrolysis. An additional 40 ml of pyridine was added, the mixture was homogenized and titrated. Each measurement was accompanied by two blank feed measurements (same procedure, but without the copolymer sample).

The acid indices were calculated as follows:

AV1 acid number (given in mg KOH/g) before hydrolysis:

AV1 =((V1 -BW) ■ © ■ 5.6106) / E, mg KOH /g

AV2 acid number (given in mg KOH/g) after hydrolysis:

AV2 = ((V2 - BW) ■ O ■ 5.6106) / E, mg KOH / g

where

V is the consumption of titrant (before hydrolysis V1 and after hydrolysis V2), e

BW is the titrant consumption for the solvents (blank feed measurement), e

© is the title factor of the holder

is the weight of the sample, g

The contents of MAA units and glutaric anhydride units were calculated as follows:

Content of glutaric anhydride units, % by weight = AV glutaric anhydride units ■ 100 / 727.9, where AV glutaric anhydride units = (AV2 - AV1) ■ 2

Content of MAA units, % by weight = AV MAA ■ 100 /651.7

where AV MAA = AV2 - AV units of glutaric anhydride

Starting materials

The following starting materials were used:

MMA, purity > 99.6% by weight from Rohm GmbH, Darmstadt, Germany

MAA, purity > 99.6% by weight from Rohm GmbH, Darmstadt, Germany

kinetic studies

The formation of glutaric anhydride units in MMA-MAA copolymers as a function of temperature and residence time was investigated.

Two MMA-MAA copolymers comprising 96 wt% and 95 wt% MMA and 4 wt% and 5 wt% MAA, respectively, were prepared on laboratory scale in a continuous stirred tank reactor, at polymerization temperature. of 140 °C, with a conversion of 45% and residence time in the reactor of 40 min. The copolymer mixture in the form of a copolymer syrup comprising 45 wt% of the copolymer was subsequently heated to 210 °C and fed to a laboratory single screw extruder with a screw diameter of 18 mm. Degassing was performed at 250 °C (cylinder temperature) at an absolute pressure of 40 mbar in the last degassing zone (vacuum zone). The copolymer melt outlet of the degassing extruder was connected directly to the melt outlet die, without conduits or melt filters.

Due to the small size of the degassing extruder and the low residence times t, the amounts of glutaric anhydride units formed in the copolymers were 400 ppm and 500 ppm, respectively. The contents of MAA residues in the copolymers were 450 ppm and 550 ppm, respectively.

Samples of the copolymers were preheated to 180 °C and then placed in an oven under a helium atmosphere and at ambient pressure at temperatures between 200 °C and 280 °C for 5 to 30 minutes. Subsequently, the contents of glutaric anhydride units and MAA residues in the samples were determined. Based on these data, an empirical mathematical model was developed for the formation of glutaric anhydride units.

The mathematical model obtained was used as a basis for additional experiments on a production scale.

Examples 1,2 (invention) and 3 (comparative)

MMA-MAA copolymers comprising 4.4 wt% and 5 wt% MAA were produced according to the following procedure.

A mixture of monomeric MMA and MAA was continuously fed to a continuous stirred tank reactor (CSTR) along with radical polymerization initiators and a chain transfer agent. Polymerization was performed at 150 °C with residence times in the reactor of 40 to 100 minutes and a total conversion of 48 to 50%. The copolymer syrup from the outlet of the CSTR was heated using a heat exchanger to about 210 to 225 °C and then fed to the copolymer syrup feeding port of the degassing extruder.

Degassing of the copolymer syrup was performed in a single screw extruder under vacuum in the last degassing zone. The unreacted monomer vapors were condensed, combined with virgin MMA and MAA, and returned to the reactor. The degassing extruder was equipped with a thermocouple in the last degassing zone that was placed 5 mm in the degassed monomer vapors above the copolymer melt to measure the temperature Tv of the copolymer melt melt in the last zone. degassing. The degassed copolymer melt was transported by the screw after the last degassing zone of the extruder with a pressure built up at the copolymer melt outlet of the extruder, then it was simply transported by pressure to the melt pipe. , to the melt filter and finally to the melt outlet die. The average pressure of the copolymer melt after the last degassing zone was approximately 40 to 70 bars (4 to 7 MPa). The copolymer melt temperature To, °C was measured at the center of the inlet of the melt outlet die.

The pressure required to press the degassed copolymer melt through the copolymer melt outlet, the melt filter and the melt outlet die was generated in the measurement zone of the degassing extruder by the extruder screw located just behind the degassing dome of the last degassing zone. The melt filter was connected by a conduit to the copolymer melt outlet of the extruder. The other side of the melt filter was connected to the melt outlet die.

The copolymer melt emerging from the melt outlet nozzle was immediately quenched with water and granulated. Subsequently, the contents of methanol residues, MAA residues, MMA residues, as well as the contents of MAA units and glutaric anhydride units in the copolymer were determined analytically as described above.

The process parameters of the degassing step in Examples 1-3 are summarized in Table 1. An experimentally determined correlation between the pressure, temperature and volume v, ml/g of a copolymer melt consisting of 95% in weight of MMA and 5% by weight of MAA, which is known from the literature, was used as a basis for the calculation of the specific volumes v, ml / g of copolymer melts in Examples 1-3. Pressure losses in the melt pipe, melt filter and melt outlet die were neglected. The specific volumes v were calculated as:

where Tv, °C is the temperature of the copolymer melt in the last degassing zone, relative to the transport direction of the copolymer melt; and

To, °C is the temperature of the copolymer melt entering the melt outlet die.

The term (1.5 . Tv + 0.5 ■ To) / 2 represents the estimated weighted average temperature between the last degassing zone of the extruder and the melt outlet die. Due to the high viscosity of the copolymer melt, low radial mixing, limited heat transfer and low thermal conductivity between the last degassing zone and the melt outlet die, the temperature difference between Tv and To is relatively small.

The residence time t is the average residence time of the degassed copolymer melt in the degassing device after the last degassing zone plus the average residence time of the copolymer melt in the volume of the melt conduit optional plus the average residence time of the copolymer melt in a volume of the optional melt filter in any volume containing optional copolymer melt containing volume plus the average residence time in a matrix of optional copolymer melt .

The residence time t between the last degassing zone and the melt outlet matrix was calculated for Examples 1-3 according to the relationship

where

Vv is the volume of the extruder filled with the copolymer melt after the last degassing zone,

where pressure buildup begins,

Vc is the volume of the melt conduit filled with the copolymer melt,

Vf is the volume of the melt filter filled with the copolymer melt,

Vd is the volume of the melt outlet die filled with the copolymer melt,

c is the melt flow,

v is the specific volume.

The content of glutaric anhydride units formed after the vacuum zone ( see Table 2) was calculated based on the methanol residues measured in the final copolymer and based on the following assumptions: The first assumption was that the content of glutaric anhydride units Units of glutaric anhydride formed after the last degassing zone of the extruder can be calculated from the content of methanol residues in the copolymer melt in the final copolymer. The second assumption was that degassing in the last degassing zone (vacuum zone) leads to a negligible content of methanol residues in the copolymer melt if the pressure in the last degassing zone is less than 300 mbar. Therefore, the complete methanol residues measured in the final copolymer were assumed to have formed during the formation of unwanted glutaric anhydride units after the last degassing zone.

The content of glutaric anhydride units formed before the vacuum zone ( see Table 2) was calculated as the difference between the content of glutaric anhydride units in the final copolymer and the content of glutaric anhydride units formed after the vacuum zone. of emptiness.

Subsequently, the formation of glutaric anhydride units observed was validated based on a mathematical kinetic model.

The following correlation was developed from the kinetics of formation of glutaryanhydride units and the evaluation of tests on a technical and production scale. This equation describes the loss factor L, in % of MAA units between the extruder vacuum zone and the melt outlet die, based on the total weight of the MAA reactor feed in stage (a ).

To minimize the loss of MAA units in the copolymer, the loss factor L should be kept low, e.g. e.g., below 8. This means that e.g. e.g., less than 8% of the MAA units in the copolymer melt are converted to glutaric anhydride units, based on the MAA in the reactor feed:

The copolymer melt temperature Tv, °C in the last degassing zone in Examples 1 and 2 (invention) was 266 °C and 265 °C, respectively. In contrast, the copolymer melt temperature Tv, °C in the last degassing zone in Example 3 (comparative) was 281 °C.

Also, the temperatures To of the copolymer entering the melt outlet die in Examples 1 and 2 (invention) were significantly lower than in Example 3 (comparative). Consequently, the term

in Examples 1 and 2 it was below 8 and in Example 3 above 8 (see Table 2).

As a consequence, the content of glutaric anhydride units in the final copolymer of Example 3 was 1.8% by weight and the methanol content was even as high as 1700 to 1800 ppm, i.e., significantly higher than in Examples 1 and 2. At the same time the content of MAA units in the copolymer of Example 3 was only 3.99% by weight, that is, significantly lower than in Example 1 of the invention. A lower content of MAA units is disadvantageous in terms of adhesion properties to metal surfaces because carboxylic groups are known to chemically interact with metal surfaces, thereby contributing to a strong adhesive bond.

A comparison between the copolymers of Examples 1 (invention) and 3 (comparative) further indicates that the copolymer of Example 1 has a higher Vicat temperature ( see Table 3). All copolymers tested had low haze and substantially no yellow cast.

Table 3. Properties of the copolymers

In summary, the copolymers of Examples 1 and 2 had a particularly high content of free carboxylic acid groups, high heat resistance and excellent optical properties, in particular low haze and substantially no yellow cast.

Examples 1-3 show that the unwanted formation of glutaric anhydride units from MAA units in the copolymer melt can be substantially suppressed while the contents of MMA and MAA residues are kept low by adjusting the melt temperature. copolymer melt Tv, °C in the last degassing zone, the temperature of the copolymer melt To, °C entering the melt outlet die and the total residence time t, s of the melt of copolymer between the last degassing zone and the melt outlet matrix of the devolatilization unit.

Claims (15)

1. A procedure for the manufacture of a molding composition comprising an oopolymer, the procedure comprising the following steps: (a) a polymerization step, in which a mixture of monomers comprising from 80.0 to 99.9% by weight, preferably from 85.0 to 98.0% by weight of methyl methacrylate; from 0.1 to 20.0% by weight, preferably from 2.0 to 8.0% by weight, of compound represented by formula (I)

the substituent R1 being a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, optionally, from 0.0 to 19.9% by weight, preferably from 0.0 to 7.0% by weight of a monomer selected from methyl acrylate, ethyl acrylate or styrene; a polymerization initiator; and, optionally, a chain transfer agent, undergoes radical copolymerization in a polymerization reactor to form a copolymer mixture comprising the copolymer and volatile components; (b) optionally, a step of heating the copolymer mixture, obtained in the polymerization step (a) at a temperature of 100 ° C to 300 ° C in a heating unit; and (c) a degassing step of removing volatile components from the copolymer mixture to form a copolymer melt in a degassing unit, the degassing unit comprising at least one copolymer mixture feed port, at least one degassing device, the degassing device comprising at least one degassing zone, at least one gas outlet at least one copolymer melt outlet, and at least one melt outlet die, in which the temperature of the copolymer melt Tv, °C in the last degassing zone, relative to the transport direction of the copolymer melt, the temperature of the copolymer melt To, °C entering in the melt outlet die and the total residence time t, s of the copolymer melt between the last degassing zone and the melt outlet die of the degassing unit are adjusted such that the term is less than 8, preferably less than 6, even more preferably less than 4, particularly preferably less than 2. 2. The method according to claim 1, wherein the term (1.5. Tv + 0.5 ■ To) /2), °C of the copolymer melt in the last degassing zone of the device Degassing in the degassing stage (c) is between 230 QC and 290 QC. 3. The method according to claim 1 or 2, wherein the total residence time t, s of the copolymer melt between the last degassing zone, relative to the transport direction of the copolymer melt , and the melt output die is in the range of 10 s to 200 s. 4. The method according to any of claims 1 to 3, wherein the degassing unit used in the degassing stage (c) further comprises at least one melt filter, located between the last degassing zone. of the degassing device and the melt outlet die. 5. The method according to any of claims 1 to 4, wherein the absolute pressure in the last degassing zone of the degassing device, relative to the direction of transport of the copolymer melt, is in the range from 100 Pa (1 mbar) to 30000 Pa (300 mbar), preferably in the range of 1000 Pa (10 mbar) to 20000 Pa (200 mbar). 6. The process according to any of claims 1 to 5, wherein the polymerization reactor in step (a) is a stirred tank reactor operated discontinuously or continuously, a tubular reactor operated continuously , a loop reactor operated discontinuously or continuously or a combination of any of them, and in which if several reactors are used, they are operated in parallel or connected sequentially. 7. The method according to any of claims 1 to 6, wherein the degassing device in the degassing stage (c) is selected from a degassing extruder, a degassing kneader and one or more instantaneous chambers. 8. The process according to any of claims 1 to 7, wherein the copolymer comprises from 80.0 to 99.5% by weight, preferably from 85.0 to 98.0% by weight of repeating units derived from methyl methacrylate; from 0.5 to 20.0% by weight, preferably from 2.0 to 8.0% by weight of repeating units derived from the compound represented by formula (I)

the substituent R1 being a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, preferably a methyl group; and, optionally, from 0.0 to 19.5% by weight, preferably from 0.0 to 7.0% by weight of repeating units derived from methyl acrylate, ethyl acrylate or styrene. 9. A molding composition obtainable by the process according to any of claims 1 to 8, the molding composition comprising a copolymer, the copolymer comprising from 80.0 to 99.9% by weight, preferably from 85.0 to 98.0% by weight of repeating units derived from methyl methacrylate; and from 0.1 to 20.0% by weight, preferably from 2.0 to 8.0% by weight of repeating units derived from the compound represented by formula (I)

the substituent R1 being a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, R1 being preferably represented by a methyl group; optionally, from 0.0 to 19.9% by weight, preferably from 0.0 to 7.0% by weight of repeating units derived from methyl acrylate, ethyl acrylate or styrene; and no more than 1.5% by weight, preferably no more than 1.0% by weight of repeating units represented by formula (II)

the substituents R2 and R3 being independently a hydrogen atom or a hydrocarbon group of 1 to 6 carbon atoms, R2 and R3 being preferably represented by a methyl group. 10. The molding composition according to claim 9, wherein the molding composition contains no more than 1400 ppm, preferably no more than 1000 ppm of methanol and/or no more than 1800 ppm, preferably no more than 1500 ppm of methacrylic acid and/or no more than 5000 ppm, preferably no more than 4000 ppm methyl methacrylate. 11. The molding composition according to claim 9 or 10, wherein the copolymer has a weight average molecular weight, determined by GPC, of 60,000 g/mol to 400,000 g/mol. 12, The molding composition according to any of claims 9 to 11, wherein the weight ratio of the repeating units represented by formula (II)

to the weight of the repeating units derived from the compound represented by formula (I)

is below 0.2, preferably below 0.1. 13. The molding composition according to any of claims 9 to 12, further comprising at least one additive selected from UV absorbers, UV stabilizers, antioxidants, colorants, flow improvers, dispersion aids, lubricants, processing color stabilizers, release aids or a combination of any of them. 14. Molded article obtainable from a molding composition according to any of claims 9 to 13 by means of a selected injection and extrusion molding process. 15. Use of a molded article according to claim 14 as a component of an optoelectronic device, preferably light emitting diode, optical sensor or a solar cell; optical element; lamp cover, light guide, optical lens, preferably for room lighting systems or automobile lighting equipment, black color column trim.